2012/1*2+2012/2*3+2012/3*4+2012/4*5+2012/5*6
=2012(1/1*2+1/2*3+1/3*4+1/4*5+1/5*6)
=2012[(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)]
=2012*(5/6)
=5030/3